The invention relates to a smoke detector with a housing formed smoke-admitting holes and having a smoke sensor and an alarm. The invention relates further to a method of checking whether the smoke holes of the detector are blocked.
Smoke detectors are known from the prior art and typically comprise a smoke sensor that can for example have an optical detection path and an alarm and that are held in a housing. Such a housing is typically mounted to a room ceiling to be able to reliably detect smoke caused by a fire. To this end, such a housing can be subdivided for example into a base that is secured to the ceiling and a cover on the lower room side that are joined together after the base is mounted to the ceiling.
For example, with an optical detection path implemented, for example, by a light-emitting element and a scattered-light sensor, it is possible to reliably detect when smoke enters the housing through the smoke holes and into the optical detection path causing light scattering therein. When this happens an alarm is triggered, which alarm can be for example be acoustic, to which end such a smoke detector of the known kind can comprise a suitable acoustic sound generator for example a piezoelement.
Besides the above-mentioned devices, smoke detectors of this known kind thus can typically comprise suitable electronics that measure the scattered light by means of a scattered light sensor to control the alarm.
It is further known from the prior art that smoke holes can be fouled or blocked so that a reliable detection of smoke can no longer be ensured. Contamination of the smoke holes can take place, for example, by dust in the air which is deposited over time in the smoke holes, or by insects such as for example spiders, or by other mechanisms. When the hole cross-section is reduced, the passage of smoke through the smoke holes is throttled and the response time of the blocked smoke detector is extended.
Smoke holes of a smoke detector can also be intentionally closed by persons. This can happen when smoke detectors are covered for example during renovation work as when painting a ceiling. In such a situation, a smoke detector is no longer reliably functional.
Furthermore, it is or will be required in the future that the proper function, therefore in particular clear smoke holes, be regularly to be checked to ensure the function capability of a smoke detector. An obligation to check concerns, for example, the operators of smoke detection systems but also the landlords of residential property where smoke detectors are installed.
The methods or smoke detectors known in the prior art all have the disadvantage that usually indirect measuring methods are used to check for free passage or the throttling degree of smoke holes.
To this end, acoustic or optical methods are frequently is used to be able to detect the contamination by measuring techniques, such methods or smoke detectors being proven to be unreliable in some cases, in particular in case of methods using acoustic measurement, in particular resonance measurement, because the acoustic behavior of a smoke detector can change not only by blockage of the holes themselves but also by internal dirt deposits in the housing of the smoke detectors or by mechanical damage of the housing which otherwise do not influence the functional capability of a smoke detector at all.